Process for hardening agglomerated bodies of ore concentrate in a high frequency alternating field

ABSTRACT

When agglomerating ore concentrates the green agglomerated bodies lack strength and hardness to be handled and charged into the reducing furnaces. The process according to the present invention resides in the hardening of the green agglomerated bodies by exposing them to a high frequency alternating field and in a further hardening treatment by exposing the bodies so treated to a hydrothermal treatment at a high temperature and at a corresponding high pressure.

United States Patent [151 3,661,554 Wijard et al. 1 May 9, 1972 [54]PROCESS FOR HARDENING 833,005 10/ 1906 Steinberg ..75/3 AGGLOMERATEDBODIES OF ORE 933,270 9/1909 Schumacher ....75/3 IN A 3,413,1[2 11/1968Dillon ....75/5 FREQUENCY ALTERNATING FIELD 3,490,895 l/] 970 Svensson..75/3

72 Inventors: Endel Wijard, Sodertalje; Jan Odsvall, FOREIGN PATENTS ORAPPUCATIONS y both of Sweden 672,137 5 1952 Great Britain .264/27 73Assignee; Akfiebohge Ehktmdius Stockholmy 517,798 2/ 1940 Great Britain..75/3

Sweden 7 Primary E.\aminerAllen B. Curtis F'led: 1969 Attorney-Young &Thompson [2|] Appl. No.: 814,191

[57] ABSTRACT [30] Foreign Application Priority Data When agglomeratingore concentrates the green agglomerated bodies lack strength andhardness to be handled and charged Apr. 1 I, 1968 Sweden ..4992 into thereducing furnaces. The process according to the [52] U S Cl 75/3 264/25present invention resides in the hardening of the green ag- [51] In} .0C2,") U20 glomerated bodies by exposing them to a hi h fre uency alter-[58] Field 264/25 Hating field and in a further hardening treatment byexposing I l I 264/273 the bodies so treated to a hydrothermal treatmentat a high temperature and at a corresponding high pressure. [56]References Cited 8 Claims, No Drawings PROCESS FOR HARDENINGAGGLOMERATED BODIES OF ORE CONCENTRATE IN A HIGH FREQUENCY ALTERNATINGFIELD When producing metal, ores of different kinds and aggregate formsare used. With the still further developed concentrating and dressingtechnique, poorer and poorer ores have come to be used and hence theyhave become still more finely ground, and therefore they are not wellsuited when in this pulverous state to be charged in the reductionfurnaces.

It has therefore been necessary to agglomerate the pulverous ore.Sintering in pans or on conveyors has been common practice to provide amanageable lumping and clustering of the ore fines. Besides requiredfuel, also other additions were made in the sinter charge, e.g. toprovide a self-fluxing sinter which means that it can be charged intothe reducing furnace without further additions, especially with respectto special slag forming constituents to provide a predeterminedcomposition of the furnace slag.

Another agglomerating process which lately has gained extendedapplication, especially for iron ore concentrates, is the production ofpellets from the concentrate by the rolling of finely ground oreconcentrate in a somewhat inclined revolving drum which is charged withore fines, humidifying agent(s), slag formers, if any, and bondingagent(s). In an untreated condition the green humid pellets thusobtained are not suited to be charged in a blast furnace, and theycannot either be handled or transported.

Briquettes which in any known manner have been produced from oreconcentrate(s), humidifying agent(s), slag former, if any, and bondingagent(s) cannot either be handled or transported withoutafter-treatment.

This after-treatment, which mainly concerns a hardening of theagglomerate, can be performed by drying, firing and/or sinteringdependent on the bonding agent mixed into the initial mixture. Storingunder humid conditions has also been proposed where hydraulic bondingagents, such as cement clinker, have been used.

In the U.S. Pat. No. 3,235,371 there is suggested the use of calciumhydroxide as bonding agent when agglomerating minerals, particularly inbriquettes made of ore concentrates, whereby the briquettes areafter-hardened by a hydrothermal treatment, i.e. a treatment with watervapor at a high pressure and a high temperature.

Ore concentrate has also been mixed with finely divided blast furnaceslag, slacked line (calcium hydroxide) and sand, and the agglomeratedbodies have thereafter been treated in steam of 120 C. succeeded bydrying in sheds wherethe bonding agent of the agglomerate dries, hardensand bonds the constituents of the agglomerate together through theinfluence of the air, as disclosed in the US. Pat. No. 3,214,263.

All the processes mentioned above require considerable time andconsiderable storing volume and could adapt themselves to a continuousproduction, it is believed, only with difficulty and at a great expense.

To impart a sufficient strength to the agglomerate immediately after andin connection to its production is of vital importance for the properhandling and transportation of the agglomerates thus produced. Here theinitially reached strength should be so high as to allow theagglomerates also to be stacked on top of each other without crushing orbreaking into fragments.

According to the present invention this problem is solved in an elegantmanner where the green agglomerates as e.g. pellets, briquettes, piecesor the like produced according to any known method out of oreconcentrate, humidifying agent, slag former and bonding agent arecarried through an alternating field of high frequency. Already within3-5 seconds in the high frequency field e.g. pellets of iron ore obtainsufficient hardness to enable the pellets to be stacked or piled inlayers of up to several decimeters in thickness.

This hardening takes place in a hitherto unexplained way, probably underthe influence of eddy currents induced in the agglomerates when they arecaused to pass through the high frequency alternating field.

According to the invention, the agglomerates are exposed to the actionof the alternating field for so long time that the temperature of theagglomerate will rise to a predetermined value, preferably below 100,particularly -95 C.

According to the invention a further hardening of the agglomeratespretreated in the alternating field takes place by submitting theagglomerates to a hydrothermal treatment at high pressure at about12.5-13 atmospheres gauge pressure and at a temperature of about 190 C.,whereby the agglomerates thus obtained acquire a strength and hardnesswithin 0.5-3 hours at said pressure and temperature, which entirelycomplies with the strength requirements for the agglomerates demanded inthe reduction and smelting processes. The time for the hydrothermaltreatment varies with factors such as the degreeof fineness of thecomponents, diameter of the agglomerates, etc.

The process according to the present invention has proved mostsuitable'andadvantageous when the agglomerates as sole bonding agentcontain granulated, finely ground slag from some metallurgical smeltingprocess. Especially good results have been reached with blast furnaceslag as only bonding agent. Agglomerates of iron ore concentrate withfinely divided blast furnace slag as sole bonding agent and treatedaccording to the process of the invention have proved to obtainexceedingly good strength and therefore have been suitable for directcharging into a blast furnace or to be used as an addition in steelmelting furnaces for the production of steel.

In order further to illustrate the process in accordance with thepractice of the present invention, the following examples are provided.It will be understood, however, that these examples are given solely forthe purpose of further illustration, and there is of course no intentionin any respect to limit the scope of the process described above, and itwill also be understood that the present invention is applicable forhardening any other agglomerate made up of any other ore concentrate ormixture of ore concentrates.

EXAMPLE 1 parts by weight of dressed magnetite ore concentrate havingthe composition shown below was dried and mixed with about 15 parts byweight of separately dried and ground blast furnace slag having a grainsize of about 2,200-3,000 cmlg.

Fe O, 94.12% Fe 71.26% mo, 4.52% Mn 0.04% MnO 0.05% P 0.10% CaO 0.11%Specific surface 950 cmF/g. MgO 0.31% Volume weight 2.6-3.3 gJcm. A1 00.27% Density 5.] gJcm. SiO 0.46% TiO 0.16% V 0 0.19% P 0, 0.02% S0.015% CO, 0.14% Na,0 0.05% K 0 0.08% CuO 0.01% Slag composition: SiO35.7% A1 0 12.4% Fe,0;, 0.7% CaO 42.8% MgO 6.5% Ratio CaO/SiO, 1.20 K 00.9% Na O 0.6% S 0.8% S0 0.1% Cl traces The mixed pulverous material wascarried on a conveyor belt to a roll disc inclined 45". Hot water (35-60C.) in an amount of 12-17 parts by weight, basis weight of oreconcentrate, was sprayed through spray nozzles located above thepelletizing disc where the addition of water is dependent on the grainsizes of the pulverous components. The soft ore pellets thus obtainedwere transferred from the disc to a conveyor belt of electricallynonconductive material, e.g. rubber or the like, the conveyor belt beingarranged to feed the pellets distributed to a spaced relationship on thebelt through a electromagnetic high frequency alternating field producedby means known per se. The main direction of the produced field washorizontally arranged relative to the conveyor belt to convey the freshpellets on the belt through the induction coil.

The high frequency device was fed with an input power of 4-6kW, and theinduction coil with a frequency of about 1 MHz. The conveying speed ofthe belt being variable, the time of treatment of the pellets could beregulated. Sufficient heating and hardening effect was obtained inpellets having l520 mm diameter after about 3-5 seconds in thealternating high frequency field.

For other ore concentrates times, other input power and frequencies ofsimilar order of magnitude may be employed. The pellets, which probablyhave been influenced by eddy currents induced therein, were transferredto low-sided, basket-like net containers or to flat-bottomed metalcases. After treatment in the high frequency alternating field, thepellets had acquired a strength to permit piling or stacking in layersseveral decimeters in thickness without any risk of I crushingprevailing. Containers of the kind filled with pellets were in theirturn piled or stacked on top of each other on a carriage provided withrollers or wheels and a batch which in practice may comprise severaltons of pellets was conveyed along for further hardening by means ofhydrothermal treatment in an autoclave.

After closing the autoclave it was filled with entirely saturated orpartially unsaturated water vapor to successively raise the pressure inthe autoclave to 12 atmospheres gauge pressure. This pressure level wasmaintained during 0.5-3 hours depending on the strength requirementsthat the end product had to comply with.

The pressure in the autoclave was then equalized to surrounding pressureby blowing off the excess pressure as rapidly as practically possible,i.e. for about 30 minutes or longer.

The examination showed that the strength of the slagbonded pelletsincreased from a few kp per pellet after the treatment in thealternating field to 60100 kp per pellet after the hydrothermaltreatment in the autoclave.

EXAMPLE 2 100 parts by weight of ore concentrate with the analysis givenbelow were mixed with 12 parts by weight of granulated and finely groundslag with an analysis as in Example 1, further with 2.5 parts by weightof finely ground limestone and 0.5 parts by weight of magnesiumcarbonate likewise ground, and the ingredients were thoroughly mixed.

Ore concentrate analysis Fe,0, 74.79% Fe 65% Fe,(), 15.49% Mn 0.18% MnO0.23% P 0.64% CaO 2.44% F 0.13% MgO 1.01% Specific surface 50 cmF/g.Al,0, 0.63% Volume weight 2.6-2.9 g.lcm." SEO, 3.39% Density 4.8 gJcm.TiO, 0.18% V,O, 0.27% P,0, 1.47% S 0.002% Na,0 0.14% K,O 0.15% 100.19%

The finely ground limestone may advantageously consist of pulverulentwaste material obtained as by-product when crushing said mineral to acertain desired lump size. For the pelletizing the finely groundlimestone should, however, be of such a fineness as to exhibit aspecific surface according to Blaine of 2,500-3,500 cm'lg to an extentof at least percent. The finely ground limestone may, if necessary, besubstituted by about 3 percent of dolomite or entirely by finely groundmagnesite. From said mixture ore pellets were produced in the same wayas in Example I. The power requirement for treatment in the highfrequency'alternating field was, however, increased by about 20 percenton account of the partially nonmagnetic constituent introduced into thismixture and owing to the reduced bonding agent content in the form ofslag, pellets were obtained whose strength was about 10 percent lowerafter the hydrothermal treatment as compared with Example 1.

Similar and equally good results have been obtained with a mixture ofdifferent ore concentrates, one of them being an iron ore concentrate,e.g. a mixture of iron ore and nickel, molybdenum, vanadium, titanium,tungsten, niobium or tantalum ore concentrates or a suitable combinationof any of them as well as with nonferrous ore concentrates or a mixtureof nonferrous ore concentrates, e.g. zinc ore concentrate or a mixtureconsisting of copper and zinc ore concentrates.

Thus the present invention has a given application to hardenagglomerates agglomerated of one ore concentrate or of mixtures of oreconcentrates.

The process according to the invention for the hardening of agglomeratedbodies, particularly pellets, briquettes or the like by first exposingthem to the influence of a high frequency alternating field andthereafter subjecting the agglomerates to a hydrothermal treatmentyields, in addition to the advantage of obtaining suitable agglomeratesfor the reduction or smelting processes at lower costs, also an indirectadvantage regarding the slag handling in the reduction processes and maybe a suitable disposition of the constituents in the agglomerates leadto an extensive reduction of the limestone or dolomite consumption,particularly in the production of pig iron out of iron ore concentrates.

' What we claim is:

1. In a process for manufacturing hard bodies from an agglomerated massof an ore concentrate also comprising a humidifying agent, a slag formerand a binding agent; the improvement comprising agglomerating said massthen exposing said agglomerated mass to a high frequency alternatingfield thereby to heat and harden said mass, and discontinuing saidexposure before the temperature of the agglomerated mass exceeds C.

2. A process as claimed in claim 1, and thereafter exposing saidhardened bodies, while still heated from exposure to said field, to ahydrothermal treatment at a temperature of about C. and elevatedpressure to harden said bodies additionally.

3. A process as claimed in claim 1, in which said ore concentrate is aniron ore concentrate.

4. A process as claimed in claim 3, in which said concentrate includesan ore concentrate selected from the group consisting of nickel,molybdenum, vanadium, titanium, tungsten, niobium, tantalum, and amixture thereof.

5. A process as claimed in claim 1, said ore concentrate being selectedfrom the group consisting of zinc and copper and a mixture thereof.

6. in a process for manufacturing hard bodies from an agglomerated massof an ore concentrate also comprising a humidifying agent, a slagformer, and as the sole bonding agent a finely divided slag obtainedfrom a metallurgical melting process; the improvement comprisingagglomerating said mass, then exposing said agglomerated mass to a highfrequency alternating field thereby to heat and harden said mass, anddiscontinuing said exposure before the temperature of the agglomeratedmass exceeds 100 C.

7. A process as claimed in claim 6, said bonding agent being a blastfumace slag.

'8. A process as claimed in claim 6, and thereafter exposing saidhardened bodies, while still heated from exposure to said field, to ahydrothermal treatment at a temperature of about 190 C. and elevatedpressure to harden said bodies additionally. 4: n a: s e

2. A process as claimed in claim 1, and thereafter exposing saidhardened bodies, while still heated from exposure to said field, to ahydrothermal treatment at a temperature of about 190* C. and elevatedpressure to harden said bodies additionally.
 3. A process as claimed inClaim 1, in which said ore concentrate is an iron ore concentrate.
 4. Aprocess as claimed in claim 3, in which said concentrate includes an oreconcentrate selected from the group consisting of nickel, molybdenum,vanadium, titanium, tungsten, niobium, tantalum, and a mixture thereof.5. A process as claimed in claim 1, said ore concentrate being selectedfrom the group consisting of zinc and copper and a mixture thereof. 6.In a process for manufacturing hard bodies from an agglomerated mass ofan ore concentrate also comprising a humidifying agent, a slag former,and as the sole bonding agent a finely divided slag obtained from ametallurgical melting process; the improvement comprising agglomeratingsaid mass, then exposing said agglomerated mass to a high frequencyalternating field thereby to heat and harden said mass, anddiscontinuing said exposure before the temperature of the agglomeratedmass exceeds 100* C.
 7. A process as claimed in claim 6, said bondingagent being a blast furnace slag.
 8. A process as claimed in claim 6,and thereafter exposing said hardened bodies, while still heated fromexposure to said field, to a hydrothermal treatment at a temperature ofabout 190* C. and elevated pressure to harden said bodies additionally.